The invention relates to the provision and improvement to the provision of information to a user of a television system by the provision of an On Screen Display (OSD) on a display screen such as that of a television set.
The generation of OSD's on television screens to provide information users is well known. However certain sequences of OSD generation operations can cause unwanted visual effects on the screen. Some known sequences of OSD deletion and creation which have been found in certain instances to cause problems include when the deletion of an OSD region occurs followed by the creation of another OSD region on screen. Secondly, a change in position of a region, followed by a drawing operation to that same region can cause problems and thirdly, changing the displayed data buffer for a region, followed by a drawing operation to the previously displayed buffer of the region, can also cause problems.
In addition to the operations indicated above, other operations may cause other situations which potentially cause unwanted effects, for instance the resizing of a region of the OSD.
Yet further, there is the problem of visual artefacts occurring under certain circumstances. Some of these circumstances can be include the updating of the OSD linked list, due to the change in time between changing the OSD linked list and the actioning of that change by processing means such as a decoder of a broadcast data receiver. The broadcast data receiver is the item of apparatus, provided integrally with the television set or connected thereto, which allows for the processing of received video, audio and/or auxiliary data from remote locations, and the processing of the same to allow video, audio and the auxiliary information, such as on screen displays, to be generated on the display screen of the television set.
In practice, the generation of such artefacts are usually avoided by waiting for the generation of a Vertical synchronization (vsync) signal to occur on the display screen after any change to the linked list has been made.
However, a problem with waiting for the vsync signal to occur before changing the OSD is that a delay in the desired change of the OSD is caused while awaiting the vsync signal and this can be irritating to the user and may, in many cases, appear, to the user at least, to be an unnecessary delay.
The aim of the present invention is to provide a method whereby upon changing an OSD, the system can, if necessary, await the vsync signal prior to the new display but, if not necessary, need not wait, thereby avoiding unnecessary delay.